300 was a glorious visual success, a cinematic transduction of an epic graphic novel into moving pictures. It proved that comic books could make money. 300: Rise of an Empire proves that money doesn’t need comic books. It’s allegedly an adaption as well, but it adapts a comic which doesn’t actually exist. Virtual items explaining the next step in a process are normally restricted to high energy physics. This is the first time they’ve happened in cinema, operating in the similar rarefied air of experts wrestling with ludicrously high numbers to work out things which will create new universes.
A sequel was guaranteed so independently of the comics we’re lucky we didn’t end up with 301, where Gandalf the White resurrects the Spartans so that they can assault Atlantis. (Wait, we’re unlucky we didn’t get that). The key point is the difference between movie and comic sequels.
A movie sequel must have the same name and basic plot, even if they don’t have the same writer, characters, or basic motivation. Ocean’s Eleven destroyed its own name in continual sequels, while the Fast and the Furious series has transcended mere numbers or continuity in a quest to constantly make money from exploding cars. Which is fine for movies where the special effects and the script are the same thing, but mercenary expansion can ruin the very idea of ending. Which is one of the most important parts of any story. Especially that of 300, a tale entirely defined by ending as epically as possible.
In comics, a successful series boosts the writer, not just the title. Comic store racks are organized by author as well as series, enabling fans to find more by creators they enjoy. While movies stretch a single premise paper-thin and wring out every last drop of money, comic creators can be funded to create new ideas with every series. Which is why we’re always interested in adaptations. But will always prefer the original material.